The state of the art contains a substantial number of patents relating to solenoids for valves, such as solenoids for fuel injectors. Typically, a solenoid valve comprises an armature that reciprocates between a first and second position for causing a valve member such as a needle to seat on and unseat from a valve seat thereby closing and opening the valve. The basic solenoid design comprises an electromagnetic coil and a ferromagnetic pole forming a stator, and a ferromagnetic armature that is connected to the valve member. The armature is kept separated from the stator by a force such as gravity, spring, or pressure.
One of the factors slowing the response time of the solenoid is eddy current generation in the ferromagnetic materials. When the solenoid is energized, eddy currents tend to inhibit the rate at which the magnetic force builds. Likewise, eddy currents tend to inhibit the rate at which the magnetic force decays upon solenoid de-energization.
Previous methods of reducing eddy currents have involved laminating the ferromagnetic material. The lamination approach, however, tends to be limited to a rectangular package. Unfortunately, fitting the lamination design into a cylindrical package like a typical fuel injector results in either a larger cylindrical package or a smaller flux path with reduced force output.
It is seen then that there still exists a need for further reducing eddy currents in a the solenoid of a cylindrically shaped valve, like a typical fuel injector.
This need is met by a low eddy current magnetic flux circuit according to the present invention, wherein a magnetically permeable wire, or filament, is toroidally wound on a tubular electromagnetic coil, and then encapsulated. The assembly is then severed into two parts, namely a stator assembly and an armature assembly.
For a fuller understanding of the present invention and its attendant features and advantages, reference may be had to the following detailed description taken in conjunction with the accompanying drawings and the appended claims.